Hydroconversion processes are important in the modern world in providing important basic fuels for everyday life. As it becomes of an increasing necessity to utilize heavier crude oil feedstocks, the oil refining industry has turned to hydrocracking processes to provide the lighter basic fuels which modern society demands. While amorphous hydrocracking catalysts are used, modern hydrocracking catalysts are often based on zeolitic materials.
Faujasite materials are one of the main zeolitic materials proposed for hydrocracking use. Early findings showed that modification of the basic materials described in U.S. Pat. No. 3,130,007 to produce a lowering of the unit cell size, gave improved selectivity to the desired middle distillate, or mid-barrel, products. To achieve this a combination of steam calcination and dealumination, usually acid-dealumination, techniques has been proposed, for example in GB-A-2,114,594; EP-A-98040; EP-A-247,679; and EP-A-421,422.
However the increased selectivity is obtained at the cost of a reduced activity, leading to a shorter catalyst lifetime, and a reduced crystallinity when the dealumination not only selectively removes aluminium but also partially destroys the faujasite crystalline structure. This in turn can reduce the available surface area and affect zeolite effectiveness.
Thus the materials documented in EP-A-421,422 which aim to be high surface area materials (also with other specific properties) have only a highest recorded surface area obtained of 752 m2/g, and have a 90% or less retained crystallinity.
In most of the dealumination treatments recorded in literature, the treatment often not only results in reduction of unit cell size but also a reduction in active surface area.